If you are at all like me you are more apt to cook eggs on mornings when the weather is cloudy and rainy. If the sun is out who wants to waste time cooking eggs and fixing a hardy breakfast. We usually assume that water boils at 212 deg. F however unless the temperature is actually measured there can be some variance. Barometric pressure as well as altitude have an effect on the boiling point of water. Low pressure will lower the temperature at which water will boil. Try your three minute egg on a clear sunny day and see if that helps.
Cap't Bob